The problem of separating and feeding sheets one at a time from a stack of sheets has been the subject of considerable development effort and considerable patent activity. Cheap, simple, and efficient solutions to the problem of multiple-sheet feeds have long been sought and even where expensive solutions are provided, the reliability of the sheet separating apparatus has never been perfect.
One of the most common types of paper feeding and separating apparatus calls for providing a mating pair of rollers through which the paper is fed. U.S. Pat. No. 2,892,629 shows an arrangement in which one of the two rollers between which the sheets pass is positively driven but the other roller is a retard roller and is not positively driven. The latter roller is freely rotatable on a shaft and is spring urged to turn in a direction opposite to that of the positively driven roller. When only one sheet is passing between the two rollers, the friction is such as to cause the retard roller to turn in the direction of motion of the sheet and against the spring bias. However, when two sheets are disposed between the two rollers, the first sheet, bearing against the positively driven roller, is advanced while the second sheet is moved to the rear, under the influence of the spring biased retard roller which now rotates in the opposite direction to sheet transfer. U.S. Pat. Nos. 3,895,790 and 3,895,782 also use the retard roller arrangement in which the retard roller is reversed when a multiple feed occurs. These prior art devices use a slip clutch system to provide forward movement when a multiple feed is not present. All of these devices depend upon the relative friction between the positively driven roller and the sheet to be advanced as being greater than the friction between the sheet to be advanced and the sheet or sheets to be returned.
It is the primary object of this invention to make use of the positively driven roller and retard roller scheme in a new and improved apparatus for the separation of multiplefed sheets in order to provide a device in which sheets are reliably fed one at a time.